The Blackstone River study area covers 83 square miles of northern Rhode Island and 5 square miles of adjacent Massachusetts (fig. 1). It includes parts of the Blackstone, Moshassuck, and Tenmile River basins, and a coastal area that drains to the brackish Seekonk and Providence Rivers. In Rhode Island, all or parts of the suburban towns of Cumberland, Lincoln, North Smithfield, and Smithfield and all or parts of the cities of Central Falls, East Povidence, Pawtucket, Providence, and Woonsocket are within the study area. Also included are parts of the towns Attleboro and North Attleborough in Massachusetts. In 1970, total population was about 240,000, which was equivalent to about one-fourth of the total population of Rhode Island. Fresh water usage in 1970 by public-supply systems and self-supplied industry was about 33 mgd (million gallons per day), which was equal to 22 percent of total fresh water use in Rhode Island for all purposes except generation of electric power (fig. 2). Anticipated increases in population and per capita water requirements are likely to cause the demand for water to more than double within the next 50 years. A significant part of this demand can be met from wells that tap the principal streams. This aquifer yielded an average of 10 mgd in 1970 and is capable of sustaining a much higher yield. The primary objectives of the study were to determine and map the saturated thickness and transmissivity of the stratified-drift aquifer and to assess the potential sustained yield of those parts of the aquifer favorable for large-scale development of water. A secondary objective was to describe ground-water quality and to evaluate the impact of induced infiltration of polluted stream water on the quality of native ground water. This report is based on analysis of drillers' records of more than 700 wells and borings which include 462 lithologic logs; 35 specific-capacity determinations; 12 aquifer tests, including detailed tests at two sites to determine streambed infiltration rates; chemical analyses of 92 ground-water and 15 stream-water samples; and geologic mapping. Selected base data are published in a separate (Johnston and Dickerman, in press). The authors are indebted to well drillers, especially American Drilling and Boring Company, R.E. Chapman Company, and Layne New England Company, for making their records available; to the water departments of the towns of Cumberland and Lincoln, for allowing aquifer tests of their well fields; to the Rhode Island Department of Health, for providing data on water quality and use; and to many other federal, state, and municipal agencies, companies, and individuals who supplied information. Their contributions are gratefully acknowledged.